Estuaries Flashcards
What is an estuary
An estuary is an inlet of the sea reaching into a river valley as far as the upper limit of the tidal rise, usually divisible into three sectors, 1. lower free connection with the open sea. 2. middle subject to strong salt and freshwater mixing 3. upper, characterized by fresh water but subject to daily tidal action.
What landscapes generally fringe the sides of an estuary
Saltmarshes and mudflats
What can be used to indicate a salt wedge profile of an estuary
Isohalines
Name three types of estuary in terms of mixing characterization
Salt wedge, Partially mixed, Well mixed
What are the energy inputs into the system that are a factor in controlling water mixing
Wind (turbulent mixing), Heating/cooling, (stratification and turnover), Tide (speed of flood tide), Gravitational circulation, (salinity gradient, density dependent mixing)
Why is classifying an estuary by its toporaphy, (eg, fjords, rias, calanques etc) not the most relavent classification
Other than bio-geography, there is very little real ecological relevance in term of the conditions provided for associated organisms.
What are the two components of salinity variation in an estuary
Spatial, longitudinal variability, (range of salinity from river to sea). Also temporal variations in salinity at any one point.
Fun Fact
Estuaries have one of the highest levels of secondary production in aquatic organisms. Tolerant deposit feeding organisms thrive from good quantity and quality of available food
Why does accretion of sediment dominate in an estuary
They have very little wave action however erosion does occur from wind, tide and storms.
What is the dependent factor of sediment size
Water column energy and wind energy
Where is most suspended fine sediment in an estuary
Turbidity maximum
What is the theoretical sediment distribution in an estuary
Cohesive sediment from upper through middle, distributing away from river flow towards sea, followed by mixed sediment in the middle to lower section, followed by sandy sediments closest to open sea
What is floc formation
Saline water +ve ions reduce repulsion of clays and aid binding of particles, biological polymers from bacteria and algae aid this process leading to high organic contect sediment aggregation
What do floc formations help to determine
Erodability, re-suspension/sedimentation therefore the transport of sediment in and out of an estuary
How do saltmarshes form?
- Accretion of sediment to form a mudflat .2. Colonisation of microalgae - cyanobacteria and diatoms.3. Colininisation by saltmarsh plants. 4. Satbilises substratum and aids further sediment accretion. 5. Forms a raised stabilised habitat patrially covered by spring high tides.
How does the first saltmarsh colonizer (Spartinia alterniflora) spread?
Asexually by means of a subterranean rhizome system
How are saltmarsh colonizers fundemental to the system
They cause the rise of the sediment surface through sediment accretion to make the habitat more terrestrial
What characteristic of saltmarsh vegetation decreases with inland zonation?
Tolerance to salinity
What is a Polychaete
A saltmarsh burrowing worm, grazer and active predator
What is an Amphipod
A saltmarsh crustacean that grazes on microalgae
What is Carcinus maenas
Portunidae - a green shore crab
What is Hydobia ulvae
A common saltmarsh gastropod
What is Littorina irrorata and what does it feed on and what is it predated by and what process is that an example of
A marsh periwinkle - feeds on Spartina, but predated by crabs, this is an example of Trophic Cascade, (top down control).
What is the DO sag?
Estuarine waters and sediments have high levels of organic material, therefore high breakdown of dissolved oxygen by aerobic bacteria in MID-ESTUARINE water - levels tend to be normal at estuary head and mouth. A DO profile would show a sag at the mid estuary area.
What biological process causes the blackening of estuarine mud?
Fine sediment prevents re-aeration by diffusion; bacterial action below the mud removes oxygen with subsequent breakdown of matter undertaken by anaerobic bacteria - this process results in toxic byproducts like CH4 (methane) and H2S, hydrogen sulphide - H2S turns mud black and produces rotten egg smell.
What effects to freshwater and saline water have on Phosphorus
P binds well to iron compounds in freshwater, transported to estuary by river and land runoff - in saline water however it binds less well and is released by diffusion in to the water column.
What is Nitrification
Nitrification is the biological oxidation of ammonia with oxygen, then into ammonium, then into nitrite followed by the oxidation of these nitrites into nitrates. Nitrification is an aerobic process performed by small groups of autotrophic bacteria and archaea
What is dentrification
Denitrification is a microbially facilitated process of nitrate reduction (performed by a large group of heterotrophic facultative anaerobic bacteria) that may ultimately produce molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products.
Name three benthic mudflat primary prodcuers
Diatoms, Cyanobacteria, seagrasses
What is the latin name for Diatoms
Bacillariophyta
What are the three main estuarine functions of diatoms
- Carbon supply to the estuarine ecosystem. 2. Produce extracellualr polymers to aid sediment stability. 3. Grazed by many invertebrate macrofauna.
Name a species of seagrass relevant to saltmarshes
Zostera spp. eg. Zostera marina
What is a Limnetic organism
freshwater organisms, cannot tolerate salinities > 0.5
What is an Oligohaline organism
freshwater organisms which occur in salinities < 5
What is a True Estuarine organism
brackish water organisms, which are found in the range 2 - 25
What is a Euryhaline marine organism
marine organisms which extend into estuaries reaching areas with salinities as low as 5. Commonest organisms in estuaries
What is a Stenohaline marine organism
marine organisms from the sea, occur in high salinity range regions > 18
What is osmoregulation
Osmoregulation is the active regulation of the osmotic pressure of an organism’s fluids to maintain the homeostasis of the organism’s water content; that is, it keeps the organism’s fluids from becoming too diluted or too concentrated.
What is an osmoconformer
Osmoconformers are marine animals which, in contrast to osmoregulators, maintain the osmolarity of their body fluids such that it is always equal to the surrounding seawater.
What is an osmoregulator
Osmoregulators actively control salt concentrations despite the salt concentrations in the environment. An example is freshwater fish. The gills actively uptake salt from the environment by the use of mitochondria-rich cells. Water will diffuse into the fish, so it excretes a very hypotonic (dilute) urine to expel all the excess water.
Give an example of an osmoconformer
Nereis diversicolor (polychaete worm)
Give an example of an osmoregulator
Upogenia spp. (mud shrimps)
What is the main difference between osmoregulators and osmoconformers
Osmoconformers are very restricted in range as cannot tolerate large salinity fluctuations. Osmoregulators are able to colinize a wider range of estuary habitats
What are the two groups of benthic deposit feeders
Selective feeders eg nematodes. Non-selective feeders, eg sedentary polychaetes
What is the importance of estuary birds to the system.
Winter and migratory populations important as may take up a high proportion of benthic invertebrate population, (top down trophic cascade).
What is the importance of estuaries for some fish other than feeding
Act as nursery grounds for some estuarine fish eg Dicentrarchus labrax (Sea bass)
